This invention relates to a method of preparing inked impression members for marking devices such as hand stamps and to means for carrying out the method.
Hand stamps and other marking devices have long been known in which the impression members as manufactured are permeated with ink so that their respective indicia or stamp elements, i.e., the protruding characters or relief elements that are to be imprinted by their use, will give the desired markings in great numbers of impressions and over long period of time without need for re-inking them.
The pre-inked impression member typically is a microporous resin structure made from a gelatinous premix, often referred to as xe2x80x9cpremixxe2x80x9d or as xe2x80x9cgelxe2x80x9d, consisting principally of heat-coalesceable thermoplastic resin particles and liquid ink. The premix is heated while confined under pressure in a molding space so that the resin particles fuse together to form a resilient microporous network that contains the ink yet is capable of releasing ink through protruding indicia of the molding when pressed against a surface to be marked.
Such impression members traditionally have been manufactured by the use of a matrix board together with metal devices termed a xe2x80x9ccasting chasexe2x80x9d. The matrix board typically is a substantially rigid board recessed on one side with sets of cavities complementary in shape to the sets of indicia, or stamp elements, required for the impression members of a plurality of hand stamps. The casting chase includes a flat metal base, a rectangular metal frame and a flat metal lid. In use, a prepared matrix board is placed onto the metal base inside its peripheral edges. The frame then is laid over marginal portions of the matrix board, protruding from them, and is clamped tightly in place, thus also clamping the matrix board onto the base, as by bolts or screws extending between confronting edge portions of the base and the frame.
Then a quantity of the gelatinous premix is poured onto the matrix board and worked into its cavities, and is followed by a further quantity to form a layer of premix filling the space over the matrix board inside the frame. Then the premix layer is overlaid by a covering means adapted to confine the layer in place, which means may comprise pliable sheet material that is either absorptive or non-absorptive to components of the premix; and the metal lid is placed on top.
Then the prepared chase assembly is placed in heating equipment, such as between heated platens of a press often called a xe2x80x9cvulcanizerxe2x80x9d, or in an oven, for a xe2x80x9ccookingxe2x80x9d or curing stage of the process. In that stage, typically, the resin particles in the layer of premix fuse together into a shaped ink-containing elastomeric structure, as mentioned above, while being held at a suitably elevated temperature and being confined in place by pressure applied to the chase assembly via the platens or plates bearing oppositely against its base and the lid.
Following the curing stage, the chase assembly may be removed from the press or oven, and cooled and opened for recovery of the cured product. During the processing, typically, some of the ink and some resin will have exuded from the premix layer into the overlaid covering material and onto some parts of the metal chase devices, and will to some extent have become integrally joined to the cured product. Consequently, it sometimes is difficult to separate the covering material and the chase devices from the cured product without tearing or otherwise marring the product. Also, time-consuming and costly cleaning operations, often with the use of solvents potentially harmful to the environment, are involved for cleaning the chase devices to prepare them for reuse with another matrix board in another molding operation.
It is an object of the present invention to provide a method and means for the manufacture of pre-inked impression members required for hand stamps and like marking devices, which can be utilized effectively by persons relatively inexperienced or untrained in such operations.
Another object of the invention is to provide a method and means for such manufacture whereby mechanical clamping or fastening operations as involved in the use of metal casting chase devices, and cleaning operations required for their reuse, may be avoided.
A further object is to provide a method and means for such manufacture whereby the confining of a layer of premix during the curing stage of the manufacturing process can be effected with little or no exudation of resin from the layer, though with some exudation of the ink and absorption of it in overlaid covering material, and whereby, after the curing, the covering means employed is easily removable from the cured layer without adhering to it so as to cause tearing or other marring of the product.
According to the present invention, a substantially rigid matrix board is formed with a molding area containing in usual manner engraved or impressed cavities complementary in shape to the indicia, or stamp elements, required for certain pre-inked impression members, and the matrix board also presents a peripheral surface area onto which an upright rigid wall means composed essentially of relatively inexpensive material and extending entirely about the molding area is adhered so as to delineate and border fluid-tight a molding space corresponding substantially in height to the thickness of the required impression members.
The molding space is filled with a premix consisting principally of heat-coalesceable thermoplastic resin particles and liquid inkxe2x80x94preferably after first rubbing such premix into the cavities in the matrix board. Then a covering means is placed over the wall means and the premix layer, for confining the premix essentially to the molding space during a curing of the premix at elevated temperature. And then, while the covering means is held in place under elevated pressure, the assembly is heated so as to convert the layer of premix into a resilient ink-containing microporous resin structure. This structure, upon being cooled and separated from the covering means and the matrix board, can be cut or otherwise subdivided into pieces constituting the required pre-inked impression members.
By virtue of the utilization of a matrix board having a peripheral surface area to which an upright wall means made of disposable, preferably biodegradable material is applied and adhered fluid-tight so as to delineate a molding space, the mechanical clamping or fastening operations involved in the use of metal chase devices are avoided. Further, the used matrix board with adhered wall means, after removal of the molded product, can simply be discarded, burned or otherwise disposed of economicallyxe2x80x94without need for any cleaning operations or any use and disposal of potentially polluting solvents as in prior practices. If on the other hand, as occasionally may happen, it is desired to duplicate or re-make a certain set of impression members, the used matrix board with its adhered upright wall means can be used again for another molding operation.
The adhered wall means can be composed, for instance, of a rigid compressed fibrous composition, such as fiberboard, or rigid strips of wood or of a biodegradable synthetic resin material, or even of a compressible material, such as a foamed plastic, if employed with rigid bearer means for limiting its compression.
According to another feature of the invention, it has been found advantageous to utilize, for covering and confining under pressure the layer of premix while it is being heated for the curing at elevated temperature, a covering means that comprises a pliable parting sheet coated on a side thereof contacting the layer of premix with a substantially resin-impermeable yet ink-permeable layer of fine particles, such, for example, as particles of emery, fine sand or other fine mineral grits, or fine glass beads, that are substantially non-adherent to the resin of the premix.
A covering means so constituted enables the curing of the layer of premix to be effected with little or no exudation of the resin, though with some exudation of the ink, from the premix layer. Further, it enables easy removal of the covering means from the cured microporous layer without causing a tear or other marring of the product. In the use of this feature, the ink exuded through the parting sheet can be collected and removed effectively by having provided additionally in the covering means suitably ink-absorbent material overlying the parting sheet, such, for instance, as a large number of layers or sheets of a readily available, inexpensive absorbent material such as newsprint or newspaper.
Other objects, features and advantages of the invention will be evident from the following detailed description and the accompanying drawings of illustrative embodiments of the invention.